1. Field of the Invention
The present application relates to sunscreen formulations, including foamable sunscreen formulations, that comprise zinc oxide and titanium dioxide particles, suitably at least 5 wt % of which have a primary particle size of greater than about 100 nm. The compositions also comprise pigments and suitably produce a minimal residual whitening effect when applied to a skin surface.
2. Background of the Invention
More than 1 million Americans are diagnosed with skin cancer each year, and many more with pre-cancerous conditions. These numbers continue to increase, not only in the United States, but worldwide. Several factors appear to be responsible for this alarming rise in skin cancer. The continual erosion of the earth's ozone layer due to pollution results in less available ozone protection than was afforded previous generations. Also, unlike previous generations, today there are over 400 medications prescribed that leave patients with an increased sensitivity to sun exposure and a heightened susceptibility to sun damage. Longer lifespan is also a contributing factor. Greater awareness, increased patient concern and better diagnosis may help to decrease this alarming rise in the rate of skin cancer.
Perhaps the most important factor in the rise of skin cancer rates is increased exposure to the ultraviolet A (UVA) wavelength, which is typically defined as 320 to 400 nanometers (nm) in the light spectrum (see FIG. 1). Previously thought of as harmless, this wavelength range is now known to contribute significantly to skin damage, skin cancer, DNA damage and immune system suppression. UVA rays penetrate the skin deeper and, unlike UVB rays (defined as the range of 290 to 320 nm, which cause initial redness and burning), damage from UVA rays is not immediately detected. Because UVA rays remain constant throughout the year and during the day, we are exposed to them continuously.
Sunscreen products are traditionally delivered to the skin in the form of creams, lotions, gels and more recently, by means of aerosol sprays or mists. Delivery of particles of titanium dioxide and/or zinc oxide by means of a spray or mist may create an inhalation hazard during application across the open air. Consequently, aerosol spray sunscreens currently use organic chemical sunscreen filters, which are solubilized in the inactive ingredients prior to delivery to the skin, but the possibility of inhalation of the sunscreen product remains.
There exists therefore a need for a readily dispensed sunscreen formulation that is easily applied to the skin, reduces or eliminates possible product inhalation, and maintains a uniform composition throughout the formulation, particularly when utilizing particulate sunscreens, e.g., zinc oxide and/or titanium dioxide.